A power source apparatus has many battery cells connected in series to increase output voltage and increase the output power. Further, to attain a high charge capacity per unit volume, a power source apparatus has been developed with battery stacks having many rectangular batteries stacked together. Battery stacks can be configured as modules, and by connecting a plurality of battery modules in series and/or parallel, power source apparatus structure can be adapted for output that meets different current and voltage specifications.
In addition, by providing a circuit board for each battery module, parameters such as battery module capacity, voltage, and battery cell temperature can be monitored and controlled for each battery module. This type of power source apparatus configured with functional modules or intelligent modules has been proposed (patent reference 1).